48. Genomic (numerical) mutations - definitions, types, human syndromes.

Question 1

Numerical chromosomes abberations:

• Abnormality of the number of chromosomes occurs as a result of their abnormal distribution during meiosis 1 or 2 (meiotic non-disjunction)
• Meiotic nondisjunction - aberration occurs in all cells of a resulting organism
• Mitotic nondisjunction - aberration in only a proportion of the cells (chromosomal mosaicism)

Answer 1

Numerical chromosomes abberations:

• Abnormality of the number of chromosomes occurs as a result of their abnormal distribution during meiosis 1 or 2 (meiotic non-disjunction)
• Meiotic nondisjunction - aberration occurs in all cells of a resulting organism
• Mitotic nondisjunction - aberration in only a proportion of the cells (chromosomal mosaicism)

Question 2

Types of numerical chromosome aberrations

polyploidy - no changed with one or several haploid complements - 3n (triploid); 4n (tetraploid)

Answer 2

Types of numerical chromosome aberrations

polyploidy - no changed with one or several haploid complements - 3n (triploid); 4n (tetraploid)

Question 3

Aneuploidy - presence of an abnormal number of chromosomes in a cell e.g. 45/47 when 46 are expected

• Monosomy - presence of only one chromosome from a pair only monosomy compatible with human life is monosomy of X-chromosome
• turner’s syndrome (monosomy is a form of aneuploidy)

Answer 3

Aneuploidy - presence of an abnormal number of chromosomes in a cell e.g. 45/47 when 46 are expected

• Monosomy - presence of only one chromosome from a pair only monosomy compatible with human life is monosomy of X-chromosome
• turner’s syndrome (monosomy is a form of aneuploidy)

Question 4

Triploidy - each chromosome is present threefold instead of twofold

Arises when an abnormal oocyte with a double (46, XX) chromosome complement instead of a haploid complement (23, X) is formed

May also arise during spermatogenesis when a spermatozoan does not contain the normal haploid complement, but rather the diploid (46, XY)

Answer 4

Triploidy - each chromosome is present threefold instead of twofold

Arises when an abnormal oocyte with a double (46, XX) chromosome complement instead of a haploid complement (23, X) is formed

May also arise during spermatogenesis when a spermatozoan does not contain the normal haploid complement, but rather the diploid (46, XY)

Question 5

Origin of trisomy and monosomy

• nondisjunction in meiosis 1/2 - one gamete is formed with an additional chromosome, whereas the other is missing a chromosome
• after fertilisation zygote contains - three copies of a chromosome (trisomy) or only a single chromosome of a pair (monosomy)

Sporadic down syndrome - trisomy 21 (47, XX +21)

Familial down syndrome - (45, XX)

Answer 5

Origin of trisomy and monosomy

• nondisjunction in meiosis 1/2 - one gamete is formed with an additional chromosome, whereas the other is missing a chromosome
• after fertilisation zygote contains - three copies of a chromosome (trisomy) or only a single chromosome of a pair (monosomy)

Sporadic down syndrome - trisomy 21 (47, XX +21)

Familial down syndrome - (45, XX)